Patent Application
20220347906
The present application claims priority of DE 10 2021 111 083.1, filed Apr. 29, 2021, the priority of this application is hereby claimed, and this application is incorporated herein by reference.
The invention relates to a method for monitoring the hydraulic supply system of an at least partially hydraulically operating plastic processing machine, in particular an injection molding machine, wherein the machine has at least one hydraulically driven axis with at least one piston-cylinder element, wherein the hydraulic supply system comprises at least one driven hydraulic pump with which hydraulic oil is delivered and fed into the at least one piston-cylinder element in order to carry out a movement of the axis.
Particularly in hydraulically driven injection molding machines (in contrast to electrically driven injection molding machines the required movements of the machine are accomplished by hydraulic piston-cylinder systems), the swivel angle or the speed of the hydraulic pump is used for control purposes. These parameters are direct factors for the pump delivery rate. Therefore, in the operation of injection molding machines, the above-mentioned parameters of swivel angle and speed are mostly used as determining elements for the piston speeds of the piston-cylinder systems, i.e. the speed of the movement of the corresponding hydraulic axis results from the specification of the swivel angle and/or the speed of the hydraulic pump.
A hydraulically operated injection molding machine is known from DE 39 19 823 A1. This machine is equipped with a control system for feedback-controlling predefined variables, such as the position, speed or force of the components used. The solution described there aims to manage the feedback-control of the drives of the machine with compact elements in order to move the relevant assemblies quickly and with low energy consumption. DE 20 2011 002 591 Ul discloses a hydraulic drive unit with which optimum efficiency is to be achieved in the operation of the drive elements, whereby required stroke volumes of hydraulic fluid can be delivered with the lowest possible energy input from the motor and pump of the system.
What was said at the beginning is also the case here if the drives of the machine are not completely hydraulic, but only partially hydraulic. In this respect, machines are also relevant here which are partially electrically driven but also have at least one hydraulically driven axis (these can be used for partial movements, for example for the ejector and the nozzle system).
The problem here is that aging of the hydraulic pump or the piston seals can lead to a reduction in speed and thus power of the hydraulically driven axis. In this case, the actual process parameters (i.e. in particular the displacement speeds of the hydraulic axes) are adversely affected during operation of the hydraulic pump by nominal values for the swivel angle or for the speed.
The invention is based on the object of further developing a method of the type described above in such a way that it is possible to monitor the condition of the hydraulic system without great effort and to determine promptly with the onset of aging processes of the hydraulic system that maintenance of the same is required.
The solution of this problem by the invention is characterized in that that, in order to monitor the aging process or an internal leakage of the hydraulic pump or a hydraulic component of the hydraulic system, it comprises the following steps:
In particular, said step b2) may comprise the substeps:
The method can be carried out for a number of partial steps of the movement of the hydraulically driven axis. The results of the individual partial steps can then be added up or averaged to arrive at the total movement of the hydraulic axis.
The operating parameter of the hydraulic pump is preferably the rotational speed of the same and/or the swivel angle of the hydraulic pump.
It is particularly preferred that the method is carried out for several hydraulically driven axes. In this case, it is particularly intended that the process is carried out for at least two of the following hydraulically driven axes: Axis for closing a mold, axis for performing an injection process of plastic melt into a mold, axis for moving an injection nozzle for plastic melt, axis for moving an ejector for a manufactured molded part.
It has proved particularly useful if the output of the result of the comparison according to step b2) above is carried out separately for several hydraulically driven axes. In this case, the functionality or efficiency can be checked in a simple manner for several parts of the entire hydraulic system.
Accordingly, a method for determining the condition of the machine's hydraulic system is provided herein.
The proposed concept aims to detect the aging or an internal leakage of the pump or a hydraulic component in a simple way. The relevant operating parameters (namely swivel angle and/or rotational speed) of the hydraulic pump, which determine the volumetric flow of the pump, are detected or recorded during each movement of a hydraulic axis and set in relation to the actual (measured) displacement speed of the hydraulic axis. To this extent, a kind of degree of efficiency of the movement of the hydraulic axis is determined during the movement of the axis.
The main movements of an injection molding machine essentially consist of the opening and closing of the injection mold, the ejector movement, the nozzle movement and the injection process.
If, for example, the degree of efficiency for the closing movement remains constant, but the degree of efficiency for the movement of the hydraulic axis for the injection process changes, an internal or external leakage of the piston-cylinder system for the injection axis can be concluded.
However, if the degree of efficiency changes for both movements (i.e. for the closing movement and the injection process), it can be concluded that a fault has occurred in the pump system.
With the proposed determination and observation of the degree of efficiency of various hydraulic axes of the machine, which is preferably carried out by appropriate software, various defects of the hydraulic system can be detected at an early stage, so that timely machine service can be initiated. Longer production downtimes of the plant are thus prevented. Troubleshooting is made easier for the service team by displaying the respective efficiency levels of the individual hydraulic axes.
For general technology concerning the delivery rate of a hydraulic pump as a function of its drive speed as well as the swivel angle, explicit reference is made to DE 10 2013 005 774 A1.
Further advantages and particulars of the present invention arise out of the exemplary embodiment described in the following and also from the associated drawings.
In the drawing:
Not shown is a hydraulic system comprising a hydraulic pump and corresponding hydraulic conduits and control or regulating elements used to cause the flow of hydraulic oil in the system.
In general, the hydraulic pump is operated at a rotational speed n and at a swivel angle α, with the two variables mentioned defining the volume flow rate Q of the hydraulic pump. The flow rate Q of the hydraulic pump is therefore determined by the speed n and/or by the swivel angle α of the hydraulic pump.
The proposed concept is based on the knowledge that the flow rate of hydraulic oil, i.e. specifically the flow rate Q (in liters/min), of the hydraulic pump supplying a hydraulic axis 2, 3, 4, 5 of the machine 1 is always in direct proportion to the displacement speed v of the axis in (mm/s).
If a nominal flow rate Q0 is assumed, which results from a measurement before bringing into service of the machine, a nominal displacement speed v0 of the corresponding hydraulic axis 2, 3, 4, 5 of the machine results from this.
If the actual displacement speed vIst of the hydraulic axis 2, 3, 4, 5 is measured during operation of the machine, a degree of efficiency η of the hydraulic axis can be determined. This is the ratio of two quotients:
η=Qunom/QuIst
with
Qu
nom
=v
0
/Q
0
as the ratio of the quotient of the nominal displacement velocity v0 to the nominal flow rate Q0 (i.e. in the unit [mm/s per liter/min])
and
Qu
Ist
=v
Ist
/Q
Ist
as the ratio of the quotient of the actual displacement velocity vIst to the actual flow rate QIst (i.e. in the unit [mm/s per liter/min]). The actual flow rate QIst is given by the measured operating parameters of the hydraulic pump, i.e. the swivel angle α and/or the speed n of the pump. The actual flow rate QIst is thus inferred or calculated from the measured actual values for the speed and the swivel angle. The correlation between volume flow rate and speed/swivel angle results from the initial determination or measurement of the pump.
By measuring the actual speeds of the hydraulic axes on one side and simultaneously measuring the operating parameters of the hydraulic pump (swivel angle and/or speed, from which the nominal volume flow Q0 can be determined by the initial determination), the degree of efficiency for each hydraulic axis can be determined and displayed (it lies between 0% and 100%). From this, a defect in the hydraulic system can be immediately concluded as soon as the efficiency falls below a specified minimum value (for example, below 95%).
If, for example, the degree of efficiency of the injection side is constantly at a high level, but the degree of efficiency of the closing side falls below the specified tolerance, it can be assumed that the pump system and the injection axis are in order, but that there is a defect (for example in the cylinder seals) in the closing system. In the opposite case, the defect would be in the injection axis.
If all efficiencies drop below a specified tolerance, it can be concluded that there is a defect in the pump system.
This is shown for an example in
In
At the top of the two Figures, it can first be seen that, given a detected speed v (in mm/s) of the hydraulic axis and a flow rate Q of the hydraulic pump, a ratio v/Q can be calculated (in mm/s per liter/min). This is the initial determination of the data before the actual operation of the machine. According to
Subsequently, the respective speed (in mm/s) and the respective volume flow rate (in liters/min) are specified for a cycle with a total of 10 substeps; the substeps are then combined to form an average value. Again, the quotient of the average speed to the average volume flow rate (in
To determine the degree of efficiency η, the quotient is formed.
In
The same procedure is followed for the injection movement of the machine as shown in
The result for the exemplary representation according to
If the degree of efficiency drops for one of the two hydraulic axes, it can be concluded that the piston-cylinder element of the relevant axis has become defective. If both efficiencies drop, however, there is a high probability that the hydraulic pump is damaged.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 111 083.1 | Apr 2021 | DE | national |
